Access systems, such as motorized lifts, have been used to transport people and cargo. These access systems include platforms, ramps, moving seats, movable steps, and the like, which may be attached to stationary structures, such as buildings and loading docks, or mobile structures such as vehicles. Access systems have been used to provide disabled individuals access to structures that traditionally were accessible only via steps or stairs, or required an individual to step over or across an obstacle. For example, motorized lifts and ramps have been used to allow disabled individuals to enter and exit vehicles. In another example, motorized lifts have been used to load and/or unload stretchers from vehicles, such as ambulances. Motorized lifts have also been used on loading docks and trucks to allow cargo to be loaded, unloaded or otherwise moved.
When an access system is installed in a vehicle, such as a minivan, it is often integrated with an original equipment manufacturer (“OEM”) or after market system (collectively, “OEM system”) of the vehicle. The OEM system may often include an electronics package with a power sliding door subsystem, a part of most OEM electronics packages, that opens or closes the sliding door when it receives a signal to do so (a “door operation signal”). Other OEM subsystems such as a remote receiver, door control subsystem (“DCS”) and a body control subsystem (“BCS”) may also be involved in opening or closing the door. These electronic subsystems are interconnected through a vehicular data communications bus which enables the BCS, DCS, remote receiver and door switch to communicate with each other and to receive a door operation signal. Generally, the user may communicate a door operation signal to the power sliding door system by pulling on a door handle of the vehicle or pushing a button on a keyless entry device. If the door operation signal is produced by a remote device, the power sliding door system receives the door operation signal via the remote receiver. If the door operation signal is produced by movement of the door handle, the door operation signal causes the door switch to close, which communicates the door operation signal to the power sliding door system.
One example of a platform of vehicles into which access systems are installed is the Dodge Caravan / Chrysler Town & Country line of vehicles. These vehicles include an OEM data bus to which a number of OEM control modules are connected. The OEM control modules transmit status and command information over the OEM data bus to control the operation of a wide variety of vehicle systems including door locks, power sliding doors, anti-lock brakes, and the like. In certain cases, if a vehicle occupant activates a button, switch, or other input to request a particular action (e.g. opening a door), one or more of the OEM control modules sends a clearance request over the OEM data bus to determine whether or not the action should be performed. After the clearance request is initiated, the OEM control modules evaluate the status of a number of vehicle systems such as the transmission position, vehicle speed, and door lock position. If the OEM control modules determine that the status of each system is acceptable, the door control subsystem will be cleared to activate the motors and switches that unlatch and open the door. On the other hand, if it would not be appropriate to open the door (e.g. because the vehicle is in motion), at least one of the OEM control modules will send a signal over the OEM data bus that prevents the door control module from opening the door.